Re:Re:encoders

Hi again;

Just some comment and questions on:

Digest Number 89,
Message: 6
Date: Tue, 13 Jul 1999 22:11:26 -0700
From: Ted Robbins <rtr@...>
Subject: Re: encoders
----------------------------
Ted wrote a long mail on encoders, and the use of exclusive or
gates. This is not that simple. You will get errors. I would like a
schematic drawing of it before I pass judgment, - but I "believe"
that you may accumulate errors - caused by mechanical jitter. To
put it very simple: Think of a simple switch. Without a debounce
circuit, you will get many pulses, - not just a clean on/off. If you
turn the encoder back 1/2 pulse length, then turn it forward again
1/2 pulse length, - any digital readout will read this as 1 step
forward, - but the position has not really changed. With very high
resolution, you may not notice this error at all, - but it can build
up.
This was just a comment, - I have a question.

> If these encoders are really simple, only one led and sensor per

channel,

> two leds and sensors, at this resolution you will not get a sine

wave, so

> you probably can't successfully increase resolution by using

differential

> op-amps to get more switch points.

This is the normal encoders, - some are more sophisticated - you get
a quasi sine wave, and usually it don't use more sensors, but a
special mask between the encoder disc and the sensor. ( it could use
more sensors too )

My question : how can you increase the resolution with differential
op-amps ? and how much ?

The normal professional circuits with state machine design as I said
in my comment, - will normally give you the option of 1,2 and 4
times the encoder counts.

To increase the resolutions with op-amps is new to me, - and I would
very much like to hear about it.

//ARNE